The harsh operating conditions encountered in an internal combustion engine, particularly the high temperatures and high pressures, cause engine components to wear rapidly. Mechanically driven actuators and actuating components are especially susceptible to wear in this environment. An actuating component-actuator interface in which the interface contact is accompanied by sliding motion is likely to experience undesirable sliding wear and sliding friction. Consequently, the materials used for producing such engine actuating components should provide good mechanical strength, thermal stability and wear resistance, particularly sliding wear resistance. Metals have typically been used to form such components. Ceramics, such as zirconia, silicon nitride, silicon carbide and the like, have been found to exhibit excellent mechanical strength, thermal stability and wear resistance. However, ceramics, despite their promise as wear-resistant engine components, are often hard and brittle and lack the formability and workability of metals which are conventionally applied to low cost precision engine components.
Composites formed from a ceramic element and a metal element have been proposed to overcome the aforementioned limitations. Although ceramic and metallic composite structures useful as internal combustion engine components are available, a ceramic-metal composite structure sufficiently reliable and durable for use as an actuating component adjusting screw element in an internal combustion engine environment has not heretofore been commercially available.
The prior art has proposed ceramic-metal composites useful in internal combustion engines that are secured together by various kinds of connecting elements. For example, U.S. Pat. No. 4,883,911 to Haahtela discloses a ceramic piston ring carrier held in place on a metal piston by casting in or with a locking ring to improve force transmission and frictional conditions between the piston and the cylinder. U.S. Pat. No. 4,848,286 to Bentz, assigned to Cummins Engine Co., the assignee of the present invention, discloses the use of an external metal connector for joining ceramic and metal components of a pivot rod. Neither of these patents, however, suggests that the arrangement described therein could be used to secure a ceramic element to a metal element to form the kind of sliding friction and sliding wear-resistant interface required in an engine actuating component which is required to transmit arcuate motion to reciprocal motion.
U.S. Pat. No. 4,966108 to Bentz et al. and commonly owned by the assignee of the present application discloses an internal combustion engine ball and socket joint assembly that includes an interface which is subject to high contact stresses, particularly those produced by highly loaded sliding contact. One of the joint components is formed of a metallic material, and the other component is formed of a high density ceramic material. The ceramic material is sintered and may include rare earth metals such as yttrium oxide or may include aluminum oxides. This construction is capable of withstanding the compressive loads experienced by an internal combustion engine ball and socket joint. However, sliding wear and sliding friction are not typically encountered in this type of joint.
U.S. Pat. No. 5,279,211 to Bentz et al., also owned by the assignee of the present invention, describes a wear-resistant metal and ceramic composite capable of withstanding the stresses produced in the interface in mechanically actuated internal combustion components such as a compression brake master piston or hydraulic tappet cam follower. The retainer structure used to hold the ceramic and metal components together in this composite securely retains the ceramic pad within the metal in a manner which prohibits relative movement between the metal and the ceramic. Some internal combustion engine actuator components, particularly components of the "elephant's foot" type designed for use in valves, valve crossheads and fuel injectors, require rotatably unconstrained attachments between actuator elements to allow them to function effectively. Therefore, the arrangement described in Pat. Nos. 4,966,108 and 5,279,211 is not applicable to such components.
Sliding friction and sliding wear present problems in several contact interfaces in internal combustion engines. Actuated members, such as engine valves, valve crossheads and unit type fuel injectors contact actuating members thousands of times each minute during engine operation. The adjusting screw assemblies associated with these interfaces tend to produce undesirable sliding friction and sliding wear at the actuated member interface, which ultimately interferes with the proper functioning of the adjusting screw assembly.
U.S. Pat. No. 5,195,489 to Reich discloses a link structure for an internal combustion engine which comprises providing a convex shape to one end of a compression release engine retarder push rod associated with a master or slave piston, while the interfacing surface of the piston is flat so that the convex end rolls rather than slides. This arrangement may minimize the need for grinding or polishing the surfaces or the need for lubrication at the interface. However, it is not suggested that any of the interfacing structures could be formed of a structural ceramic to address problems arising from wear and heat generation by friction at the interfacing surfaces.
Problems commonly associated with sliding friction include parasitic loss, heat generation and frictional forces, which prevent optimum engine function. For example, the sliding friction loss between the rocker levers and valve crossheads in a heavy duty diesel engine can be 0.5 HP (horsepower). This loss, which is equivalent to a reduction in brake specific fuel consumption (b.s.f.c.) of 0.2%, generates heat that must be removed by the engine's cooling system. Friction forces generated in the type of sliding contact that occurs between a rocker lever and valve crosshead are transferred to the adjacent valve components. This produces additional sliding friction, wear and component failure.
Sliding wear can produce a range of problems from cosmetic surface deterioration to loss of mechanical set or calibration to the increased likelihood of catastrophic failure of the worn component, which prior art ceramic and metal composite structures available for internal combustion engines have not solved.
The prior art, therefore, has failed to provide a ceramic-metal composite for an internal combustion engine component which provides a loose attachment of the ceramic element to the metal element in a way that permits rotatably unconstrained movement between the ceramic and metal elements and substantially reduces sliding wear and sliding friction. A need exists for such a ceramic-metal composite, particularly for internal combustion engine adjusting screw assemblies.